A polymer electrolyte fuel cell (hereinafter, referred to as PEFC) is configured to cause an electrochemical reaction between a fuel gas containing hydrogen and an oxidizing gas containing oxygen such as air, thereby generating electric power and heat at the same time. A single cell of PEFC includes: a MEA (Membrane-Electrode-Assembly) including a polymer electrolyte membrane and a pair of gas diffusion electrodes (an anode and a cathode); gaskets; and electrically conductive plate-shaped separators.
Main surfaces of the separators are provided with manifold holes (reaction gas supply manifold holes and reaction gas discharge manifold holes) forming manifolds serving to supply and discharge the fuel gas and the oxidizing gas (these gases are referred to as reaction gases). Among the main surfaces, those in contact with the gas diffusion electrodes are provided with groove-shaped serpentine reaction gas channels, through which the reaction gases flow and which are in communication with the manifold holes.
There is a known fuel cell separator and a fuel cell in which such serpentine reaction gas channels include a turn portion provided with a recess in which a power generation gas is mixed. In the recess, a plurality of island-shaped projections rising from the bottom surface of the recess are arranged (see Patent Literature 1, for example).
In the fuel cell separator and the fuel cell disclosed in Patent Literature 1, the projections are arranged on the extension of channel grooves, and therefore, the power generation gas can be suitably mixed.